This work covers two distinct features: the factors responsible for the ideal use of intravenous feeding mixtures and the study of biorhythms, circadian cycles, in man. Although these two subjects may ultimately become closely related (since feeding clues may be of great importance to circadian oscillations and to the utilization of that food) the two researches are being conducted separately at the present time under the direction of Dr. Francis D. Moore and Dr. Martin Moore-Ede. The work on feeding is conducted on normal fasting man and on surgical patients; we have documented the interaction of substrates in normal fasting man under circumstances of starvation, starvation with glucose at various levels with glycerol and with fat emulsion. We then carried out extensive studies of the utilization of a mixture of amino acids alone. To this have been added the following substrates: low dose glucose, high dose glucose, gyerol and fat emulsion. These are the first documented experiments in which comparable sets have been carried out with these substrate mixtures. The findings indicate that the addition of further energy sources greatly accelerates and improves the utilization of infused amino acids in man. The work on circadian rhythm (biorhythms) has been carried out in the acclimatized squirrel monkey preparation. We have shown that there are several distinct oscillators in the body; desynchronization of these oscillators has profound effects on the animal including loss of temperature control. Light-dark cycles and the provision of feeding by mouth are important time clues. A wide variety of other clues including activity, social interaction and fluid administration have no effect. The circadian rhythm work is of major importance in the acclimatization of man to rapidly moving environments (air or in outer space). It is evident thht they may also have a major effect on the utilization of intravenously infused food substances.